Hydraulic cam shaft phase adjusters are typically supplied with engine lubricating oil which serves as a pressure medium in the phase adjuster for adjusting the phase position of a cam shaft relative to a driving crankshaft of an internal combustion engine. The phase adjuster adjoins the lubricating oil cycle of the engine and is therefore supplied with the lubricating oil via the so-called main oil separator of the lubricating oil cycle. Despite cleaning in the main oil separator, it is common to arrange a filter screen in the phase adjuster in order above all to keep original dirt away from the phase adjuster.
EP 2 578 818 B1, which incorporated by reference. discloses arranging a filter screen in the region of the pressure port of a control valve of the phase adjuster. Arranging filter sleeves around the working ports of the control valve is also known. Since the installation spaces are small and there is simultaneously a requirement for as little pressure loss as possible, but also because of a requirement for the mechanical stability of the filter screen to be sufficient, filter media which are used include metal fabrics, plastic fabrics or thin perforated (metal) sheets. The mean mesh size or aperture width of the screen apertures is significantly above 100 μm and typically around 200 μm and more. Despite cleaning in the main oil separator and in the phase adjuster, malfunctions in the phase adjuster and frictional wear on the parts of the phase adjuster which can be moved relative to each other are a problem.
Through systematic experiments using different dirt mixtures, so-called misuse experiments, the inventors have discovered that even solid particles having particle dimensions of less than 100 μm cause frictional wear, above all on the hydraulic functional components of the control valves and on the bearing of the magnetic anchors of the electromagnetic valve actuators, and also directly cause malfunctions in these components of phase adjusters. There is for example the danger of such particles leading to a blockage of the valve piston in a control valve of a phase adjuster. Sand and corundum particles have also in particular proven problematic. During the production of engines, such particles can enter the oil channels of the cylinder crankcases as casting sand and blasting material and, despite the lubricating oil in the main oil separator being cleaned and despite the filter screens additionally arranged in the phase adjusters, have a certain statistical likelihood of leading to malfunctions in the phase adjuster.